1. Field of the Invention
The present invention generally relates to a power semiconductor device and, more particularly, to the power semiconductor device having at least one temperature detector incorporated therein.
2. Description of the Prior Art
The power semiconductor device is generally known as used to deal with a relatively high electric power and does therefore evolve a relatively large amount of heat. In order to protect the power semiconductor device from being overheated, importance has come to be recognized to provide the semiconductor device with an overheat protection. For this purpose, the power semiconductor is generally provided with a temperature detector on the same substrate where semiconductor elements are formed, to thereby monitor the temperature of the substrate. The prior art power semiconductor device having such a temperature detector incorporated therein will be discussed in detail with particular reference to FIGS. 11 and 12.
As shown in FIG. 11, the power semiconductor device identified by 50 includes a power semiconductor element 80 such as, for example, an insulated gate bipolar transistor (IGBT) and a temperature detector 60. This temperature detector 60 employed in the power semiconductor device 50 is made up of two diode elements 70 and 71 formed on a p-type region 52 of the substrate 51 with a insulating layer 54 intervening therebetween. As shown in an equivalent circuit diagram in FIG. 13, the diode element 70 is used for detecting the temperature of the substrate and is connected in forward biased fashion between an anode 62 and a cathode 64, whereas the diode element 71 is connected in reverse biased fashion between the anode 62 and the cathode 64 for cramping a reverse voltage which may be generated in, for example, a control circuit. In detecting the temperature of the substrate, this temperature detecting diode element 70 generally relies on the temperature dependency of the forward going voltage VF between the anode 62 and the cathode 64.
In practice, the reverse voltage cramping diode element 71 does not require the temperature dependency to be taken into consideration and, therefore, a single diode is employed therefor for minimizing a space occupied thereby on the substrate. On the other hand, temperature dependent change of the forward going voltage VF between the anode 62 and the cathode 64 of the temperature detecting diode element 70 is relatively small and, therefore, for the temperature detecting element 70, a plurality of diodes connected in series with each other are generally employed to increase the temperature dependent change. By way of example, FIG. 13A illustrates, in a schematic plan view, the power semiconductor device in which the temperature detecting diode element 70 is comprised of two diodes 70a and 70b and the reverse voltage cramping diode element 71 is comprised of a single diode. FIG. 13B illustrates a cross-sectional representation taken along the line Dxe2x80x94D in FIG. 13A. In this power semiconductor device shown in FIGS. 13A and 13B, respective portions of the insulating layer 54 positioned immediately beneath the diodes 70a, 70b and 71 have an equal thickness.
It has, however, been found that the temperature detector 60 employed in the above described power semiconductor device 50 is susceptible to an erroneous operation that is brought about by external noises such as, for example, unwanted external electromagnetic waves and is therefore limited in application. Specifically, since the power semiconductor device 50 has parasitic capacitances, a difference occurs between an electromotive force generated in a forward going path of the diode element 70 and that generated in a negative going path of the diode element 71 when the temperature detector 60 is interfered with an external electromagnetic wave, resulting in an erroneous operation.
The parasitic capacitances referred to above will be discussed in detail. As discussed above, FIG. 12 is an equivalent circuit diagram of the power semiconductor device 50 shown in FIG. 11. Regions 56 and 58 of different conductivities opposite to each other that form the diode elements 70 and 71, respectively, of the temperature detector 60 confront the p-type region 52, which is a base region of the power semiconductor device 80, through the insulating layer 56. Considering that this p-type region 52 is held at a potential which is the same as the emitter potential and that the diode elements 70 and 71 forming respective parts of the temperature detector 60 are formed on the insulating layer 56, a parasitic capacitance C1, C2, C3 and C4 is formed between the base region 78 and each of regions of respective conductivities of the diode elements 70 and 71.
Hitherto, the presence of the parasitic capacitances C1 to C4 has not been recognized. In contrast, the inventors of the present invention have found that the presence of those parasitic capacitances brings about detrimental problems to the proper functionality of the temperature detector used in the power semiconductor device. By way of example, since the regions of the two different conductivities forming the respective diode elements have respective surface areas that are generally different from each other, the parasitic capacitances on respective sides of each of the diode elements are of different values, that is, C1xe2x89xa0C2 and C3xe2x89xa0C4. Also, where the two diodes 70a and 70b are connected in series with each other to form the temperature detecting diode element as shown in FIG. 13A, the total capacitance generated between the diodes 70a and 70b and the base region 78 of the power semiconductor element 80 amounts to twice that generated between the reverse voltage cramping diode element 71 and the base region 78, that is, C1=2xc3x97C3 and C2=2xc3x97C4. Because of this, when an external noises such as the external electromagnetic wave interfere with the power semiconductor device 50, a difference occurs between an electromotive force generated in the forward going path of the diode element 70 and that generated in the negative going path of the diode element 71 as hereinbefore described, resulting in an erroneous operation. A similar difference occurs even between an electromotive force generated in a circuit between the diode 70a and the cramping diode 71 and that between the diode 70b and the cramping diode 71, resulting in an erroneous operation.
The Japanese Laid-open Patent Publications No. 8-236709, No. 10-116987 and No. 58-25264 discloses a semiconductor device in which a power element and a heat sensitive element formed on a common semiconductor substrate with an insulating layer intervening therebetween to prevent a parasitic action of the heat sensitive element. Even in the power semiconductor devices disclosed in those publications, since the heat sensitive element confronts the semiconductor substrate through the insulating layer, parasitic capacitances tends to be formed in a manner as discussed hereinabove. However, none of those publication address to the problem associated with the parasitic capacitances.
Accordingly, the present invention has been devised to provide an improved power semiconductor device having a temperature detector incorporated therein, which is substantially free from an erroneous operation which would otherwise be brought about under the influence of an external noise such as an external electromagnetic wave.
In accordance with one aspect of the present invention, there is provided a power semiconductor device which includes a power semiconductor element formed on a substrate and a temperature detector including a temperature detecting diode element having at least one diode formed on the substrate for detecting a temperature. The temperature detecting diode has two regions of conductivity types different from each other. Also, a capacitance formed between one of the regions and a base region of the semiconductor element is substantially equal to a capacitance formed between the other of the regions and the base region.
A surface area of one of the two regions confronting the base region of the semiconductor element is preferably equal to that of the other of the two regions confronting the base region.
In one preferred embodiment of the present invention, the temperature detector may also include a reverse voltage cramping diode element having a diode for cramping a reverse voltage. In this case, the temperature detecting diode and the cramping diode are connected in reverse biased fashion to each other.
In another preferred embodiment of the present invention, the sum of capacitances between the regions of the temperature detecting diode and the base region may be substantially equal to the sum of capacitances generated between the regions of the cramping diode.
In a further preferred embodiment of the present invention, total area of the temperature detecting diode confronting the base region may be substantially equal to the total area of the cramping diode.
In a still further preferred embodiment of the present invention, the temperature detecting diode element may include a plurality of diodes connected in series.
In a still further preferred embodiment of the present invention, the temperature detecting diode may be formed opposite the base region through the insulating layer. Consequently, the first ratio between total area against the base region and thickness of the insulating layer in the temperature detecting diode may be substantially as large as the second ratio between total area against the base region and thickness of the insulating layer in the cramping diode.
According to the power semiconductor device of the present invention, the power semiconductor device includes a temperature detector including a temperature detecting diode element having at least one diode for detecting temperature formed on the substrate, on which a power semiconductor element is also formed. The temperature detecting diode has two conductive regions of conductivity types different from each other. Also, a first capacitance generated between one region and the base region of the semiconductor element is substantially equal to a second capacitance formed between another region and the base region. Therefore, the difference from first electromotive force and second electromotive force may be substantially eliminated, so that the temperature detector will not operate erroneously.
According to the power semiconductor device of the present invention, two conductive regions of the temperature detecting diode have area opposite the base region of the semiconductor element as large as each other. Then, the capacitance generated between each region and the base region may be as large as each other. Therefore, the difference from first electromotive force and second electromotive force may be substantially eliminated, so that the temperature detector will not operate erroneously.
According to the power semiconductor device of the present invention, the diode for cramping reverse voltage may be connected between the anode and the cathode in a reverse biased fashion in the temperature detector with respect to the temperature detecting diode. Therefore, the reverse voltage generated between the cathode and the anode may be cramped and be changed within area of predetermined value.
According to the power semiconductor device of the present invention, the total capacitance summed from capacitances generated between the regions of the temperature detecting diode and the base region of the cramping diode may be substantially as high as the total capacitance summed from capacitances generated between the regions of the cramping diode and the base region. Therefore, even if any noise from outside, e.g. magneto-electric jamming will trespass into the power semiconductor device, difference between one electromotive force generated in the circuit of the temperature detecting diode and another electromotive force generated in the circuit of the cramping diode may be substantially eliminated, so that the temperature detector will not operate erroneously.
According to the power semiconductor device of the present invention, the total area of the temperature detecting diode confronting the base region may be substantially as large as the total area of the cramping diode. Then, the total capacitance summed from capacitances generated between the regions of the diode for detecting temperature and the base region of the cramping diode may be substantially as high as the total capacitance summed from capacitances generated between the regions of the cramping diode and the base region. Therefore, even if any magneto-electric jamming will trespass into the power semiconductor device, the difference between one electromotive force generated in the circuit of the temperature detecting diode and another electromotive force generated in the circuit of the cramping diode may be substantially eliminated, so that the temperature detector will not operate erroneously.
According to the power semiconductor device of the present invention, the temperature detecting diode element may include a plurality of diodes connected in series with each other. Therefore, the voltage VF between the anode and the cathode in the forward direction may be amplified, so that temperature may be detected at high precision.
According to the power semiconductor device of the present invention, the temperature detecting diode may be formed opposite the base region through the insulating layer. In addition, the first ratio between the total area against the base region and thickness of the insulating layer in the temperature detecting diode may be substantially as large as the second ratio between the total area against the base region and thickness of the insulating layer in the cramping diode. Then, the total capacitance summed from capacitances generated between the regions of the temperature detecting diode and the base region of the cramping diode may be substantially as high as total capacitance summed from capacitance generated between each region of the cramping diode and the base region. Therefore, even if any magneto-electric jamming will trespass into the power semiconductor device, difference between one electromotive force generated in the circuit of the temperature detecting diode and another electromotive force generated in the circuit of the cramping diode may be substantially eliminated, so that the temperature detector will not work erroneously.